1. Field of the Invention
The present invention relates to DC-DC converters.
2. Description of the Related Art
FIG. 1 illustrates a conventional DC-DC converter that transforms an original DC voltage VDD to a transformed DC voltage Vout and outputs Vout by a transformed DC voltage output terminal. The conventional DC-DC converter comprises an inductance L, a PWM signal generator 102 (where PWM is an abbreviation of Pulse Width Modulation), a Power MOS enable signal generator 104, a Power MOS 110, a driver 106 for the PMOS transistor Mp of the Power MOS 110, and a driver 108 for the NMOS transistor Mn of the Power MOS 110.
The transformed DC voltage Vout is divided by resistors R1 and R2 that are coupled in series. The divided transformed DC voltage is inputted into the PWM signal generator 102 to generate a PWM signal Vswitch. The Power MOS enable signal generator 104 comprises a DTC 112 (where DTC is the abbreviation of Dead-Time Controller) and a ZCD 114 (where ZCD is the abbreviation of Zero Current Detector). The DTC 112 outputs a PMOS transistor enable signal SW_P and the ZCD 114 outputs an NMOS transistor enable signal SW_N. When the PMOS transistor enable signal SW_P is in its enable state (low), the driver 106 pulls the PMOS transistor enable signal SW_P to ground to completely turn on the PMOS transistor Mp. When the NMOS transistor enable signal SW_N is in its enable state (high), the driver 108 pulls the NMOS transistor enable signal SW_N to the original DC voltage VDD to completely turn on the NMOS transistor Mn. The transformed DC voltage Vout, therefore, is maintained within a stable region.
In general, conventional DC-DC converters are designed based on specifications provided by manufactures of loads, and thus the power consumption of the DC-DC converter is predetermined. The predetermined power consumption is usually designed as the maximum possible value under which the load can operate normally. However, when the load is a processing unit, RAM, monitor and so on, or devices that are usually in a stand-by mode (light load), the actual power consumption is far lower than the predetermined value. Thus, the conventional DC-DC converter with light load has very poor power transform efficiency.